Not really important, but useful ability to mark topic as important or simply highlight the topic. Not pinned, it will act as a normal topic but highlighted.

Like an announcement of sort, update, or letting people know something important.

This is just an example, it can be other colors or different fas fa:

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Currently, we already have three statuses: locked (red), pinned (yellow), and solved (green). If a post is truly important enough to be pinned, we can already pin up to three posts. If it's not that important, it can just remain a normal post — no need for this.

The best solution would be to have predefined tags or labels for posts. That would work like categories, and they would be useful for finding specific posts among many others.

Like I said, not that important. More like optional addon. No big deal.

On Mobile View:

Another not important observation is mobile view topic. Take a look.

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It's is as big as the post it self. Maybe user card can be 2 columns instead of every object on new line. Feels like you are reading post, user card, post, user card. All the focus should be on post. Kind of like you have on main page:

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Something to consider 👍

And again the padding on mobile view 25 is too much. We need to utilize all the available space proper. 10px is plenty.

.post-form
 {
    margin: 30px auto;
    padding: 25px;
    background: var(--surface);
    border-radius: var(--radius);
    border: 1px solid var(--border);
}